1. Field of the Invention
This invention relates to a method of construction of the top slab of a nuclear containment building
2. Related Art
In the procedure for constructing a nuclear containment building (hereinafter referred to as the building), there have been two traditional methods of constructing the top slab on top of a cylindrical wall (hereinafter referred to as the wall) structure.
A method of construction will be explained in reference to FIG. 7. In an area bounded by the wall 1, a floor slab 3 and the shield wall 2 of the pressurized reaction vessel (not shown), a plurality of support columns 4 are built to support radially-arranged support beams 4a which, in turn, act as a support for a slab support 6. After installing reinforcing members, the top slab 7 is poured, as illustrated by a dotted line in FIG. 7.
Another method of constructing a top slab in an area sectioned off by the wall 1, a floor slab 3 and the shield wall 2 of the pressurized reaction vessel is explained with reference to FIG. 8. In this method, support components 9 and 10 are first constructed on the top sections of the wall 1 and shield wall 2. A plurality of large beams 11 are spanned across radially said components 9 and 10 in between the upper and lower steel reinforcements (hereinafter referred to as upper and lower reinforcements) of the top slab 7. Said large beam 11 are supported by means of hanging bolts 12 and anchors 13a which are welded to the back side of the slab liner 6. The top slab 7 is formed by pouring concrete as indicated by dotted lines in FIG. 8.
Practising of these procedures presents the problems of installation as described in the following.
In the method of FIG. 7, the support columns 4 and 4a sustain the stresses imposed by the slab liner 6, the weight of the reinforcements and the concrete as well as the stresses accompanying installation activities. However, the floor spaces on said floor slab 3 are limited because of a large number of facilities, such as other equipment and piping, which are already installed inside the building. Consequently, it becomes difficult to place said columns in all of the optimum positions to support the loads imposed by the heavy section top slab and accompanying installation activities. Furthermore, integral fastening metal components at the bottom surfaces of the slab liner 6 mechanically interfere with the top surfaces of the support column 4 at the points of contact with the said supports. In addition, this technique requires a large number of columns and trusses to be temporarily erected on top of the floor slab 3, and upon completion of the installation of the top slab 7, all of the said columns and beams need to be removed from the interior of the building. However, as stated earlier, much of the interior spaces are already filled with various equipment, and it is extremely difficult to secure open paths to dismantle and transport such masses of residual materials.
In the method of FIG. 8, on the other hand, a load supporting member is constructed by pouring concrete in the spaces available in beam 11. However, because of the limited distances between the upper and lower reinforcements in top slab 7, the substantial height of said beam 11 becomes restricted and approaches that of a full web beam, and therefore, the elasticity of the top slab 7 presents a problem. This technique has an additional problem of not being able to optimize positioning of the load-bearing components of the top slab, such as beam 11, hanging bolts 12, liner anchor 13a, on the one hand, and the reinforcements within the top slab 7, on the other.